1. Technical Field. The present disclosure relates to systems and methods for controlling an internal combustion engine having at least one spark plug per cylinder with ionization signal sensing feedback to manage high dilution and lean air/fuel ratios.
2. Background Art. Manufacturers continue to improve control of internal combustion engines to enhance fuel economy and performance while reducing emissions using more sophisticated sensing and processing hardware and software. To improve control of the combustion process, ionization signal sensing (or ion sense) uses a bias voltage applied across a sensor positioned within the combustion chamber to generate a signal indicative of the combustion quality and timing. For spark-ignition engines, one or more spark plugs may be used as an ion sensor with the bias voltage applied across the air gap of the spark plug, or between a spark plug electrode and the cylinder wall.
Various strategies are being investigated to increase power density and downsize engines, i.e. provide smaller, lighter engines with power equal to or greater than more conventional larger and heavier engines. For example, lean air/fuel ratio operation, and cooled external exhaust gas recirculation (EGR) on turbocharged or supercharged engines may be used to increase power density. Typically, these smaller engines operate at higher loads where pumping losses are reduced to further improve fuel economy. However, combustible mixtures supplied to the engine cylinders with high levels of dilution and lean air/fuel ratios are more difficult to ignite and to achieve complete combustion. Previous strategies included increasing ignition energy by using larger spark plug gaps, raising the ignition coil output, and/or sparking multiple times. While these approaches may be suitable for some applications, increased ignition energy may lead to premature spark plug wear and gap erosion resulting in associated combustion performance degradation, which may adversely impact fuel efficiency, drivability, and/or feedgas emissions.